The present invention is directed to combinations of a β-lactamase inhibitor with sulbactam and, optionally, imipenem/cilastatin. The combinations are useful for the treatment of bacterial infections, including infections caused by drug resistant organisms, including multi-drug resistant pathogens. More particularly, the invention relates to a combination of β-lactamase inhibitor compound 1: or a pharmaceutically acceptable salt thereof, with sulbactam, or a pharmaceutically acceptable salt thereof, and, optionally, imipenem/cilastatin, or a pharmaceutically acceptable salt thereof.